Teens, young adults may drive flu epidemics: study

NEW YORK (Reuters Health) - Little kids, with their runny noses and dirty hands, might be unfairly vilified for their role in spreading sickness, suggests a new study.

The research, published in the American Journal of Epidemiology, hints instead that teens and young adults may be the main drivers of seasonal and pandemic flu.

Flu cases tended to peak in Canada in the 10-to-19 and 20-to-29 age brackets before the disease topped out in older adults or young kids during seasonal and pandemic flu outbreaks -- meaning prevention in this age group may be crucial to slowing the transmission of flu on a bigger scale, researchers say.

"It definitely jibes with the rest of the literature," John Brownstein, from Children's Hospital Boston, told Reuters Health.

"Broadly speaking there's a recognition of the importance of the under-18 group in terms of their spread of influenza early in the epidemic," said Brownstein, who has studied flu epidemics but was not involved in the new work.

Led by Dena Schanzer of the Public Health Agency of Canada, researchers collected data from positive lab tests for the flu compiled by the Canadian government each year. Then they graphed the number of flu cases in kids and adults of different ages over the course of each flu season, allowing them to see when the flu peaked in each group, and which group "led" the epidemics.

In the years between 1995 and 2006, the researchers found that seasonal flu peaked in the 10-to-19- and 20-to-29-year-olds about one week earlier than it did in older adults and young kids.

And during the 2009 H1N1 epidemic, flu cases hit their peak in preteens and teens a few days before other groups as well.

Schanzer and colleagues wrote that they didn't have enough data to figure out why teens and young adults might have been leading flu outbreaks in Canada.

Some studies have also found that preschoolers might lead the way in getting and spreading the flu. And the authors say that targeting young kids with flu vaccination programs could still help cut down on the spread of flu.

But researchers speculate that school-age kids and young adults might have more close contact with a greater number of peers than very young kids.

"The really small kids, they're certainly extremely susceptible (to the flu) in general, but they're not as mobile and they don't congregate in as large a group as middle school and high school kids do," said Ira Longini, who studies infectious diseases at the University of Washington School of Public Health in Seattle.

It may be the same with young adults, who also tend to be socially active, he said.

But in general, "what we believe happens is these outbreaks start in the schools and rapidly get into families and then radiate out from there to the workplaces and other settings," Longini, who was not involved in the current study, told Reuters Health. "It's really households and schools that drive these epidemics."

Every year, between five percent and 20 percent of Americans get the flu, contributing to some 36,000 deaths. To stop the spread of the virus, Longini said that elementary, middle and high school-age children need to be the target of flu-prevention efforts.

"We need to use vaccines effectively and early in the season to vaccinate school children," he said. "We just need to do that every fall if we want to slow (the transmission of) influenza."